1. Field of the Invention
In general, the present invention relates to the structure of seals that are used around rotating shafts. More particularly, the present invention relates to the manner and method by which such shaft seals are manufactured.
2. Description of the Prior Art
The prior art is replete with machines, equipment and component parts that require a seal be formed around a rotating shaft. As such, over the years, many shaft seal designs have been developed for a wide array of rotating shaft applications. Many shaft seals, such as those used on automobile engines are designed as part of the engine and are actively lubricated and cooled by the running of the engine. However, in many applications, shaft seals are needed in isolated applications where active lubrication and cooling are either not available or are not desirable.
Two of the most common families of isolated shaft seal designs are packed seals and positive pressure seals. Typically, neither packed seals nor positive pressure seals require active lubrication or cooling. A packed seal is the type of shaft seal used in most plumbing valve fixtures. With a packed seal, packing material is placed around the shaft and the packing material is compressed against the shaft until the packing material is so dense that foreign material cannot pass through the packing material. Such shaft seal designs work well but add significant friction to the rotating shaft. Accordingly, such shaft seals are typically only used with shafts that turn only on occasion or rotate at very low speeds. If such packed seals were used on shafts that turn quickly, the friction would rapidly heat the seal to a point where the seal or shaft would fail.
Positive pressure shaft seals add much less friction to a rotating shaft than do packed seals. Accordingly, positive pressure seals can be run at much higher shaft rotation speeds without concerns of friction heat causing the seal to fail.
Referring to FIG. 1, a typical prior art positive pressure seal assembly 10 is shown. In the prior art, an elastomeric seal 12 is clamped directly onto a rotating shaft 14. The elastomeric seal 12 is interposed between two wear rings 16 that have smooth external faces. The wear rings 16 and the elastomeric seal 12 are placed in an annular housing 18, wherein the interior of the housing 18 is kept above ambient pressure. As the shaft 14 turns, the elastomeric seal 12 on the shaft 14 turns, as do the wear rings 16 surrounding the elastomeric seal 12. The wear rings 16 move against the interior of the housing 18. Foreign material is prevented from entering the seal by the contact of the wear rings 16 against the interior of the housing 18 and the positive pressure within the housing 18.
Although positive pressure shaft seals have many advantages over packed seals, they tend to be significantly more expensive than simple packed seals. One of the most extensive elements in a positive pressure shaft seal is the wear ring. The wear rings are typically machined from solid blanks of stainless steel. Each wear ring has a complex internal configuration that enables the wear ring to engage and retains the elastomeric seal. Furthermore, the wear rings have external surfaces that must be polished smooth to reduce wear friction. It is the cost of properly manufacturing the wear rings that often is a limiting factor in economically producing positive pressure shaft seals.
A need therefore exists for an improved way to produce wear rings in a positive pressure shaft seal that reduces both the cost and complexity of manufacture. This need is met by the present invention as described and claimed below.